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Arrays

Hard

  • Given a set of rectangles represented by a height and an interval along the y-axis, determine the size of its union. (Solution)
  • Given an array, find the longest arithmetic progression. (Solution)
  • Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
    • E.g. [100, 4, 200, 1, 3, 2] => 4. Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4. Note: Your algorithm should run in O(n) complexity. (Solution)

Medium

  • Given a list of item prices, find all possible combinations of items that sum a particular value K. (Solution)
  • Given an array of integers find whether there is a sub-sequence that sums to 0 and return it. (Solution)
    • E.g. [1, 2, -3, 1] => [1, 2, -3] or [2, -3, 1]
  • Trapping rain water: You have an array with the heights of an island (at point 1, point 2 etc) and you want to know how much water would remain on this island (without flowing away). (Solution)

Easy

  • Implement a circular buffer using an array. (Solution)
  • Given an array of integers, print out a histogram using the said array; include a base layer (all stars) (Solution)
  • Given an array and an index, find the product of the elements of the array except the element at that index. (Solution)
  • Given 2 separate arrays, write a method to find the values that exist in both arrays and return them. (Solution)
  • Given an input array and another array that describes a new index for each element, mutate the input array so that each element ends up in their new index (Solution)
    • Discuss the runtime of the algorithm and how you can be sure there would not be any infinite loops
  • Given an array of non-negative numbers, find continuous subarray with sum to S. (Solution 1) (Solution 2)
  • Given an array of numbers list out all triplets that sum to 0. Do so with a running time of less than O(n^3). (Solution 1) (Solution 2)
  • Given an array of numbers list out all quadruplets that sum to 0. Do so with a running time of less than O(n^4). (Solution)
  • Given an array of integers, find the subarray with the largest sum. (Solution)
  • Find the second maximum value in an array. (Solution)
  • Rotate an array by an offset of k. (Solution)
  • Remove duplicates in an unsorted array where the duplicates are at a distance of k or less from each other. (Solution)
  • Given an unsorted list of integers, return true if the list contains any duplicates within k indices of each element. Do it faster than O(n^2). (Solution)
    • Given an unsorted list of integers, return true if the list contains any fuzzy duplicates within k indices of each element. A fuzzy duplicate is another integer within d of the original integer. Do it faster than O(n^2).
    • E.g. If d = 4, then 6 is a fuzzy duplicate of 3 but 8 is not.
  • Say you have an unordered list of numbers ranging from 1 to n, and one of the numbers is removed, how do you find that number? What if two numbers are removed? (Solution)
  • Given an array of string, find the duplicated elements. (Solution 1) (Solution 2)
  • Given an array of integers, find a maximum sum of non-adjacent elements. (Solution 1) (Solution 2)
    • E.g. [1, 0, 3, 9, 2] should return 10 (1 + 9).
  • Given an array of integers, modify the array by moving all the zeroes to the end (right side). The order of other elements doesn't matter. (Solution 1) (Solution 2)
    • E.g. [1, 2, 0, 3, 0, 1, 2], the program can output [1, 2, 3, 1, 2, 0, 0].
  • Given an array, return the length of the longest increasing contiguous subarray. (Solution 1) (Solution 2)
    • E.g., [1, 3, 2, 3, 4, 8, 7, 9], should return 4 because the longest increasing array is [2, 3, 4, 8]
  • Given an array of integers where every value appears twice except one, find the single, non-repeating value. Follow up: do so with O(1) space. (Solution)
    • E.g., [2, 5, 3, 2, 1, 3, 4, 5, 1] returns 4, because it is the only value that appears in the array only once.

Other

  • In an array of arrays, e.g. given [[], [1, 2, 3], [4, 5], [], [], [6, 7], [8], [9, 10], [], []], print: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.
    • Implement an iterator that supports hasNext(), next() and remove() methods.
  • Paginate an array with constraints, such as skipping certain items.
  • Given array of arrays, sort them in ascending order.
  • Given an array containing only digits 0-9, add one to the number and return the array.
    • E.g. Given [1, 4, 2, 1] which represents 1421, return [1, 4, 2, 2] which represents 1422.